WHY NOT JUST USE SEARCH?

An index is not simply a list of words found in the text, or a listing of keywords. It provides access to all relevant topics, regardless of the exact wording used. It is well-known that relying on search alone normally provides many irrelevant or insignificant results, and often misses out on many relevant references.The scale of the mismatch between search terms and actual content can be significant. In a recent case study I did, I compared search results and the index to try to access topics that I knew were covered in two books.The number of search results in itself was daunting – often over 50, and sometimes over 100. How many readers will have the time and patience to sift their way through so many hits? If they do invest the time, chances are they will be disappointed with what they find. As many as five sixths of the search results in my case study did not lead to a discussion relevant to the topic. The highest success rate was slightly over half.Imagine looking at 55 search results to find 9 of interest –or ploughing through 135 search results to find only 19 of interest! You might think that, with so many search results, at least you aren't going to miss anything. You would be wrong. I also investigated from the other direction: how many of the relevant discussions would have been found using only the search function .

The best coverage was obtained for a term that really has no substitutes and is difficult to discuss without that term: coal.

In the other comparisons, the proportion of relevant references missed was as high as three quarters.My investigation also suggested that search is more likely to underrepresent important topics and discussion. These are more likely to be referred to by a range of different terms, or simply considered to be understood.This makes sense – a skilled author will try to avoid using the same term over and over. For example, instead of repeating "debt" over and over, the author of one of my case study books used terms like indemnity, damages, amount due, amount owed, liability; often, no synonym was used at all, the topic was simply understood.I also found that for longer passages, the highlighted search term often did not occur until late on in the passage – for example, on the fourth page of a six page discussion. People might well start reading from that point onwards, missing much of the discussion.